In a motor and a motor drive device, a drive torque is generated by flowing a current through a motor coil. When a large current continuously flows through the motor coil, the motor coil generates heat, which may reach a high temperature, such as equal to or higher than 180° C., and cause a fault, such as breakage of the motor coil or demagnetization of a motor magnet. Therefore, the motor coil needs to be protected by, for example, measuring its temperature to limit the current flowing through the motor coil. However, because it is physically difficult to provide a temperature sensor directly on the motor coil, it is necessary to estimate the temperature of the motor coil by some other possible methods.
In a conventional motor-coil temperature estimation method for a motor drive device, for example, as described in Patent Literature 1, the temperature detected by a temperature sensor provided in the periphery of a motor, and a low-pass filtered value of an integral of a value obtained by multiplying a square value of a motor current by a gain are added together to estimate the temperature of the motor coil.